4,597 research outputs found
ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters
Versatile standardized pulse modulation nondissipatively regulated control signal processing circuits were applied to three most commonly used dc to dc power converter configurations: (1) the series switching buck-regulator, (2) the pulse modulated parallel inverter, and (3) the buck-boost converter. The unique control concept and the commonality of control functions for all switching regulators have resulted in improved static and dynamic performance and control circuit standardization. New power-circuit technology was also applied to enhance reliability and to achieve optimum weight and efficiency
Local control of multiple module converters with ratings-based load sharing
Multiple module dc-dc converters show promise in meeting the increasing demands on ef-
ficiency and performance of energy conversion systems. In order to increase reliability,
maintainability, and expandability, a modular approach in converter design is often desired.
This thesis proposes local control of multiple module converters as an alternative to using
a central controller or master controller. A power ratings-based load sharing scheme that
allows for uniform and non-uniform sharing is introduced. Focus is given to an input series,
output parallel (ISOP) configuration and modules with a push-pull topology. Sensorless
current mode (SCM) control is digitally implemented on separate controllers for each of the
modules. The benefits of interleaving the switching signals of the distributed modules is
presented. Simulation and experimental results demonstrate stable, ratings-based sharing
in an ISOP converter with a high conversion ratio for both uniform and non-uniform load
sharing cases
Optimal PWM switching strategy for single-phase AC-DC converters
The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase
AC-DC converter-fed traction drives. The objective is to eliminate low-order supply
current harmonics, including those injected into the supply due to load-side current ripple.
Other advantages that the switching strategy has to offer over phase-control include
improved supply power factor, reduced VA consumption for a given demand speed and
load, reduced torque and speed ripple and smaller armature circuit smoothing inductance.
The effect of field current boost on the dynamic response of the drive is also described.
It is shown that field boost helps to reduce the speed rise-time by increasing the
electromagnetic torque available during acceleration periods.
Closed-loop control of a 4-quadrant DC drive is described and a comparison made between
the performance of PID-control and pseudo-derivative feedback control. It is shown that
pseudo-derivative feedback control has several advantages to offer, amongst which are ease
of tuning of the controller gains and a superior performance following load torque
disturbances.
A laboratory size drive system was designed and built, and used to validate simulation
predictions for both the switching strategy and pseudo-derivative feedback control. A
microcontroller based hardware implementation of both the switching strategy and a digital
pseudo-derivative feedback controller was adopted, with the switching strategy being
implemented using an off-line approach of precalculating the switching angles and storing
these in look-up tables.
The armature voltage controller comprises a dual-converter employing IGBTs as switching
devices. The use of IGBTs allows higher switching frequencies at significant power levels
than would be possible if GTOs were used. It also simplifies the gate drive circuit design
and minimises the need to use snubber circuits
Grid integration of renewable power generation
This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation.This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation
Adaptive prediction in digitally controlled buck converter with fast load transient response
An adaptive prediction scheme based on linear extrapolation for digitally controlled voltage-mode buck-type switching converter is presented. A major drawback of conventional digitally controlled switching converters is bandwidth limitation due to the additional phase lag in the digital feedback control loop. By predicting the future error voltage, the ADC sampling time delay is compensated in order to achieve a higher bandwidth even with a modest sampling rate. Both simulation and measurement results show that the output voltage settling time of the digitally controlled buck converter is reduced by as much as 28% with the proposed adaptive prediction. The fastest settling time in response to a 600mA load transient is around 15μs, approaching the transient response of the state-of-the-art analog-based controller.published_or_final_versio
Multi-functional model predictive control with mutual influence elimination for three-phase AC/DC converters in energy conversion
© 2019 by the authors. Conventional model predictive control (MPC)-based direct power control of the three-phase full-bridge AC/DC converter usually suffers from the parametric coupling between active and reactive powers. A reference change of either the active or reactive power will influence the other, deteriorating the dynamic-state performance. In addition, the steady-state performance affected by one-step-delay arising from computation and communication processes in the digital implementation should be improved in consideration of switching frequency reduction. In combination with the proposed novel mutual influence elimination constraint, this paper proposes the multi-functional MPC for three-phase full-bridge AC/DC converters to improve both the steady and dynamic performances simultaneously. It has various advantages such as one-step-delay compensation, power ripple reduction, and switching frequency reduction for steady-state performance as well as mutual influence elimination for dynamic capability. The simulation and experimental results are obtained to verify the effectiveness of the proposed method
Control analysis and design of medium voltage converter with multirate techniques
This work aims to unify the current knowledge about multirate controllers with design
techniques for grid-tied converters, in this occasion, connected to Medium Voltage AC grid. Therefore, the multirate contributions, that have been given so far, are studied, as
well as everything related to modulation techniques for power converters. The temporal
implications of the DSPWM actuator will be correlated to multirate analysis, in
addition to possible alternatives for applications with a lower sampling frequency than
modulation one. Finalizing with explanations and result demonstrations of controllers
working between two frequencies or rates, by means of the available power converter in laboratory.Este trabajo pretende unir el conocimiento actual sobre controladores multitasa o
multifrecuencia (multirate) con técnicas de diseño para convertidores conectados a la red, en este caso concreto, a la red alterna (AC) de Media Tensión. Por tanto, se
estudian las contribuciones multirate realizadas hasta la fecha, asà como todo lo relacionado con la modulación de la señal de control para los convertidores. Las
implicaciones temporales del actuador DSPWM se relacionarán con el análisis
multitasa, asà como se explicarán posibles alternativas para aplicaciones con una
frecuencia de muestreo menor que la de modulación. Finalizando con la explicación y
presentación de resultados de controladores trabajando entre dos frecuencias o tasas,
mediante simulaciones del convertidor disponible en laboratorio.Máster Universitario en IngenierÃa Industrial (M141
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